This invention relates to a method and a device for driving a lens shutter which is particularly built in a lens to be equipped on a single-lens reflex camera with or without a focal plane shutter.
In a single-lens reflex camera, a focal plane shutter has no mechanical connection with components on a lens side and therefore provides a large freedom in design of lenses in comparison with the lens shutter, thereby enabling construction of interchangeable lens to be simplified. Moreover, the focal plane shutter is able to shut off film surfaces with ease and to obtain higher shutter speeds in comparison with lens shutters. Therefore, the focal plane shutter is mainly used for single-lens reflex cameras capable of using interchangeable lens.
On the other hand, however, the focal plane shutter has a relatively narrow range in synchronism with an electronic flashing. In photographing subjects moving at high speeds, moreover, there is a risk of images being distorted with the focal plane shutter. Therefore, it has been desirable for the single-lens reflex camera to be able to use interchangeable lenses having shutters built therein which do not have the above disadvantages.
However, a hitherto used single-lens reflex camera having a focal plane shutter does not have driving means for a lens shutter. Therefore, when the camera body is equipped with an interchangeable lens having a lens shutter built therein, charging the focal plane shutter on the side of the camera body by winding-up has been effected separately from charging the lens shutter in the interchangeable lens.
In such a method of driving lens shutters, it is necessary to charge a lens shutter on the side of the interchangeable lens manually as well as winding-up on the camera body every time when photographing. Therefore, there is a difficulty in operation and a photographing operation is often carried out erroneously without charging the lens shutter, so that photographing is impossible at a valuable shutter chance.
In order to avoid such disadvantages, in addition to focal plane shutter charging means, lens shutter charging means may be provided on the camera body. With such an arrangement, however, the construction on the side of the camera body is considerably complicated, making the camera to be bulky and expensive and causing various troubles in operation.
Moreover, Japanese Patent Application Publication No. 51,786/86 discloses driving means for driving a lens shutter built in an interchangeable lens to be provided on a single-lens reflex camera having no focal plane shutter. This lens shutter includes swing levers concentrically urged in a direction opposite to a setting direction, and a setting ring for setting the swing levers against the urging forces. When the setting ring is rotated in the setting direction against the urging forces, the shutter is set and after an iris and shutter blades are opened, the swing levers are anchored at the set positions, while only the setting ring is rotated in the reverse direction to its original position.
When a release is effected, the swing levers are released so as to be rotated in the direction opposite to the setting direction by the urging force, and after the shutter blades are closed and the iris is stopped down to a set value, the lens shutter is released to open and close the shutter blades in a set time.
With the driving means disclosed in the Japanese Patent Application Publication No. 51,786/86, the setting ring is driven in normal and reverse directions by a reversible motor as a driving source provided on a lens board integrally connected to the lens shutter.
Moreover, an engaging lever for anchoring the swing levers set by the setting ring is provided with a first engaging portion for anchoring the swing levers at a set portion, and a second engaging portion for once stopping the swing levers on the way of rotation in the direction opposite to the setting direction. A release magnet is provided to actuate the engaging lever into an engaging position and is connected to a power source in series with a switch which is turned on by pressing a shutter button and with a switch which is turned off on an upward pivotal movement of a light cut-off plate. With this arrangement, the swing levers set by the setting ring are returned by turning the magnet on, and on the way of the returning movement, the swing levers are once stopped at the second engaging portion of the engaging lever. The engagement of the swing levers is released on the upward pivotal movement of the light cut-off plate to effect the shutter release.
In the driving means disclosed in the Japanese Patent Application Publication No. 51,786/86, the motor rotatively drives in the normal and reverse directions the setting ring which in turn drives in the setting direction the swing levers. However, the swing levers are rotated in the opposite direction in returning movement by a spring force without being driven by the motor.
Accordingly, it is required to provide the engaging lever for anchoring the swing levers against the urging force and the release magnet for actuating the engaging lever against the urging force in the anchoring direction. Moreover, owing to shocks upon returning of the swing levers there is a risk of the engaging lever being damaged which engages the swing levers on the way of returning, thereby making impossible the engagement between the engaging lever and the swing levers. Furthermore, a shock on releasing the shutter may cause a camera movement.
Therefore, it is considered that a preferable method is to build the motor for driving the lens shutter in a lens barrel which is electrically connected to the camera body.
A lens barrel having a motor built therein has been disclosed in Japanese Laid-open Patent Application No. No. 57-186,738 wherein a motor is located on an outer side of the barrel in the proximity of iris means where light rays converged so that an axis of the motor is parallel with an axis of a lens shutter.
Although such an arrangement of the motor is effective for a lens barrel having no lens shutter, a longitudinal end of the motor will interfere with diverging light rays. Therefore, it is very difficult to arrange the motor on the lens barrel.